Annular flow channel section for a turbomachine

ABSTRACT

An annular flow channel section for a turbomachine is provided. The annular flow channel includes a guide vane ring having a number of guide vanes which are arranged next to each other in the circumferential direction, each guide vane including a vane base, a platform and an airfoil that projects into the flow channel in a radiating pattern. The flow channel is delimited on the platform side by shielding elements, each of which being disposed between two immediately adjacent airfoils, wherein the shielding elements are arranged on the platforms for creating a particularly space-saving flow channel section while creating a gap, and impingement-cooling openings are provided in the platform.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2010/058352, filed Jun. 15, 2010 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 09008227.2 EP filed Jun. 23, 2009. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention refers to an annular flow passage section for a turbomachine, having a stator blade ring which has a number of stator blades arranged in series in the circumferential direction and in each case comprising a blade root, a platform and a blade airfoil which projects radially into the flow passage, the flow passage being delimited on the platform side by shielding elements which are seated in each case between two directly adjacent blade airfoils.

BACKGROUND OF INVENTION

An annular flow passage section, which is referred to in the introduction, is known from EP 1 219 787 B1, for example. In detail, the printed patent specification discloses a ring of cast stator blades of an axial flow turbine, in which the stator blades have an aerodynamically curved blade airfoil, provision being made in each case for platforms on the radially outer (root-side) end and radially inner (tip-side) end of the blade airfoil. Installed in the turbine, the platforms are covered by ceramic heat shields. The heat shields are designed in such a way that in pairs they cover a platform half of two directly adjacent stator blades in each case. The heat shields therefore extend basically from the suction-side wall of the blade airfoil of a first stator blade to the pressure-side wall of the blade airfoil of a second stator blade. The ceramic heat shield is fixedly connected in this case, via a tongue, to the gas turbine blade so that the heat shield is fastened with capability of being exchanged. A construction for fastening such a cover, which is alternative to this, is disclosed in US 2007/0237630 A1.

Ceramic heat shields, however, require a comparatively large wall thickness in order to be able to durably and reliably withstand the temperatures of the hot gas which occur in a stationary gas turbine. If such ceramic heat shields are used both on the tip-side platform and on the root-side platform of stator blades, this leads to comparatively large turbine stator blades with correspondingly increased space requirement, which also increases the production costs.

The use of a shroud consisting of a superalloy is also known from US 2007/0237630 A1. Such shrouds, however, are comparatively cost intensive.

In addition, a modular turbine blade with two sheet-metal covers, which, in addition to the associated platform half, also covers the transition to the aerodynamically curved blade airfoil in each case, is known from EP 1 557 535 A1. The sealing of the gap between abutting platform halves of adjacent turbine blades by means of a sealing element inserted in grooves is disadvantageous in this case, however. A form of delimiting the flow passage, which differs from this, follows from EP 1 557 534 A1. It is shown therein that a platform half of the arrangement known from EP 1 557 535 A1 can be dispensed with if one of the sheet-metal covers is supported on the adjacent turbine blade. For that reason, one platform half can be dispensed with. In the case of this development, a close contact of the sheet-metal cover on the adjacent turbine blade is not always ensured however.

SUMMARY OF INVENTION

The object of the invention is therefore the provision of an annular flow passage section for a turbomachine, which requires comparatively little space and, furthermore, guides the hot gas flowing in the flow passage section in a particularly reliable and safe manner, for a particularly long period, without premature wear phenomena occurring on the components which border on the flow passage.

The object is achieved with an annular flow passage section for a turbomachine, in which the shielding element is arranged on the platforms, forming a gap, and impingement cooling holes are provided in the platform for impingement cooling of the shielding elements.

The invention is based on the knowledge that the platform halves, which are fanned on the stator blades, can also then be protected against the hot gas and its corrosive and thermal influences if the shielding element does not consist of ceramic. In this case, the shielding element is then to be cooled to an adequate degree. For the purpose of cooling, according to the invention, it is provided that impingement cooling of the shielding element is used. As a result of the cooling of the shielding element, this can be designed with thinner walls than in the case of the prior art. The comparatively thin-walled design of the shielding element saves space and is also more cost-effective. The blade airfoil of corresponding stator blades can consequently be of a shorter design in its span without reducing the flow cross section of the annular flow passage section compared with the flow passage section which is known from the prior art.

Stator blades, which are used in the flow passage section according to the invention, are customarily produced in a casting process and are therefore mainly in one piece. Since the platforms or platform halves of such stator blades previously had to withstand not only the pressure of the hot gas but also had to transmit the mechanical load—caused by the flow forces—of the blade airfoil onto a rear-side hook-fastening, these previously had comparatively solid walls, i.e. large wall thicknesses. This led to poor coolability of platforms, as a result of which the service life of such stator blades was previously also limited by the platforms. By using a shielding element according to the invention, especially the thermal load of such platforms can be reduced, which leads to a significant extension of the service life of stator blades.

Particularly in the case of flow passage sections in which stator blades without shielding elements were used, especially in the region of a hollow fillet-like transition from the platform to the blade airfoil, moreover, a mass accumulation occurred as a result of a corresponding rounding, which mass accumulation was only able to be cooled to an inadequate degree. As a result of the inadequate coolability of the transition, fatigue phenomena like cracks also occurred at these points. By using shielding elements, the transition can now be better protected against the direct contact and influence of the hot gas which flows in the flow passage since at this point there is now a gap between the shielding element and the blade airfoil wall or transition, through which gap the cooling medium which is used for the impingement cooling of the shielding element—for example cooling air after completion of the impingement cooling—can discharge into the flow passage. Also, this leads to an extended service life of the stator blade due to the reduction of the thermal load in the region of the transition from the platform to the blade airfoil.

In this case, each shielding element extends across a gap which is delimited by the platforms of two directly adjacent stator blades. This enables a low-loss guiding of the hot gas in the flow passage, even in the event that a displacement of mutually adjacent platforms occurs on account of thermally induced expansions.

Further advantageous developments are disclosed in the dependent claims.

The shielding elements preferably have in each case a baseplate, consisting of a metallic material, which delimits the flow passage and is produced separately from the stator blades. As a result of the cooling of the shielding element, recourse can be made to metallic materials. Moreover, the entire shielding element is produced separately from the stator blades. This has the advantage that in the event of wear phenomena occurring on the shielding element only this is to be replaced and not the complete stator blade, as in the case of unshielded stator blade platforms.

The shielding element is preferably produced from a metallic material with good insulating properties.

According to a further advantageous development, the wall thickness of the baseplate is less than the wall thickness of the platform which is covered by the shielding element. The thinner the walls of the shielding element are, the better this can be cooled by means of the impingement cooling. Furthermore, by using a comparatively thin-walled shielding element a flow passage section which is compact in respect to space requirement can be disclosed, which reduces the production costs and material costs for such a flow passage section.

According to a preferred development, provision is made on the edges of the baseplate for transversely arranged wall sections which can be connected to the sidewalls of the platforms. As a result of this, an expedient fastening of the shielding element on the stator blade can be brought about.

In order to further increase the thermal resistibility of the shielding element in relation to the hot gas, it can be advantageous if the shielding element has a protective coating, especially a thermal barrier coating, on the flow passage side.

BRIEF DESCRIPTION OF THE DRAWINGS

The further explanation of the invention follows based on the exemplary embodiment which is represented in the drawing.

In the drawing:

FIG. 1 shows a section through two of the blade airfoils of an annular flow passage section as a developed view thereof, with a shielding element arranged over the platforms of the stator blades, and

FIG. 2 shows the section according to the line of intersection II-II through the platform of the stator blade and through the shielding element.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows the cross section through the blade airfoils 14 of two stator blades 10 of an annular flow passage section 12 of a turbomachine, for example a gas turbine, through which hot gas can axially flow. The flow passage section 12 essentially comprises a stator blade ring with a large number of stator blades 10 which are arranged in series in the circumferential direction. Of the stator blade ring which is known in many cases in the prior art, only two of the stator blades 10 are shown in FIG. 1. The stator blades 10 in this case are fastened on a stator blade carrier in a conventional manner. The view in FIG. 1 is selected so that the blade airfoils 14 are shown in cross section and therefore a plan view of the platforms 16 of the stator blades 10 results. A shielding element 22 is arranged in a form-fitting manner between a suction-side blade airfoil wall 18 of the stator blade 10 which is shown further down in FIG. 1 and the pressure-side blade airfoil wall 20 of the stator blade 10 which is shown further up in FIG. 1. The shielding element 22 is essentially, i.e. on the hot gas side, formed in one piece and completely covers the subjacent halves of the platforms 16 between the blade airfoils 14 of the two directly adjacent stator blades 10. For the sake of clarity, only one of the shielding elements 22 which are arranged in the flow passage section 12 is shown. In principle, the stator blade ring has such a shielding element 22 between each pair of directly adjacent blade airfoils 14 in each case, wherein adjacent shielding elements 22, moreover, on one side butt against each other upstream of a leading edge 21 of the blade airfoil 14 and downstream of a trailing edge 23 of the blade airfoil 14 with a gap which is as small as possible.

In addition, impingement cooling holes 24 are arranged in the platforms 16, for example in a grid-like manner. FIG. 2 shows the section according to the line of intersection II-II through the stator blade 10 and the shielding element 22. In FIG. 2, features which are identical to FIG. 1 are provided with identical designations. The shielding element 22 is arranged on the platform 16 on the hot gas side, forming a gap, provision being made in the platform 16 for impingement cooling holes 24 which extend obliquely, for example, to its surface. During operation of the turbomachine, a cooling medium K is fed to the rear space 28 facing away from the flow passage 26, which cooling medium can discharge from the rear space 28 through the impingement cooling holes 24 and in a jet-like manner can enter the gap between the shielding element 22 and the platform 16. With the impingement of the impingement cooling jets, these cool the shielding element 22 so that despite the hot gas which flows through the flow passage 26 this shielding element has an adequate service life.

The shielding element 22 which is shown in cross section in FIG. 2 consists of metal and essentially comprises a baseplate 30 which extends parallel to the passage-side platform surface. On the two edges of the baseplate 30 which lie opposite each other, provision is made for wall sections 32 which at the sides project transversely to the baseplate 30 and encompass corresponding sidewalls of the platform 16 in a clamp-like manner. The wall thickness of the baseplate 30 is significantly less in this case than the wall thickness of the platform 16 in the region of the impingement cooling holes 24.

For fastening the shielding element 22 on the stator blade 10 or on the platform 16, this can be screwed on, for example, as shown by the dash-dot lines. Other types of fastening, such as clamping, especially form-fitting clamping of the shielding element 22 on the platform 16, are also conceivable. If necessary, the shielding element 22, on its surface which is exposed to the hot gas, can have a thermal barrier coating in order to further increase its thermal resistance.

The cooling medium K, which flows into the gap between the shielding element 22 and the platform surface, flows out at that gap 36 (FIG. 1) which is provided between the shielding element 22 and the suction-side blade airfoil wall 18 or pressure-side blade airfoil wall 20 after impingement cooling has been carried out.

The platform 16 which is shown in FIG. 2 and the shielding element 22 which is arranged above it in this case can be both a root-side platform and a tip-side platform of stator blades 10, providing the stator blades 10 which are used in the annular flow passage section 12 have platforms 16 which extend transversely to the blade airfoil 14 at both opposite ends of the blade airfoil 14. Naturally, the invention can also be used on only one of the two platforms 16 of such a stator blade 10.

In all, by using the invention an annular flow passage section 12 for a turbomachine is disclosed, the flow passage section having a stator blade ring which has a number of stator blades 10 arranged in series in the circumferential direction and in each case comprising a platform 16, and a blade airfoil 14 which projects radially into the flow passage 26, wherein the flow passage 26, on the platform side, is delimited by shielding elements 22 which are arranged in each case between two directly adjacent blade airfoils 14, wherein for forming a particularly space-saving flow passage section 12 the shielding elements 22 are arranged on the platforms 16, forming a gap, and impingement cooling holes 24 are provided in the platform 16. 

1-5. (canceled)
 6. An annular flow passage section for a turbomachine, comprising: a stator blade ring including a plurality of stator blades arranged in series in a circumferential direction and each stator blade comprises: a blade root which is provided for the fastening, at least one root-side platform with two platform halves, and a blade airfoil which projects radially into the flow passage, wherein the flow passage, on the platform side, is delimited by a plurality of shielding elements, of which one shielding element in each case is arranged between two directly adjacent blade airfoils, butting against these, and covers a gap which is delimited by the platform halves of directly adjacent stator blades, wherein the plurality of shielding elements are arranged on the platforms, forming a gap, and wherein a plurality of impingement cooling holes are provided in the platforms for impingement cooling of the plurality of shielding elements.
 7. The flow passage section as claimed in claim 6, wherein the plurality of shielding elements include in each case a baseplate, consisting of a metallic material, which delimits the flow passage and is produced separately from the plurality of stator blades.
 8. The flow passage section as claimed in claim 7, wherein a first wall thickness of the baseplate is less than a second wall thickness of the platforms which are covered by a shielding element.
 9. The flow passage section as claimed in claim 7, wherein provision is made on the baseplate for transversely arranged wall sections which are connected to sidewalls of the platforms.
 10. The flow passage section as claimed in claim 8, wherein provision is made on the baseplate for transversely arranged wall sections which are connected to sidewalls of the platforms.
 11. The flow passage section as claimed in claim 6, wherein each shielding element includes a protective coating on the flow passage side.
 12. The flow passage section as claimed in claim 9, wherein each shielding element includes a protective coating on the flow passage side. 